Level 19, in which you hop from level to level with fireballs underfoot and a blueish background, is pretty hard. The simplest way to pass it is to wait for a bird to fly at you from the left, hop up as it swoops at you, then "ride" it across the screen to the right until you get past the hard parts by hopping to the right on each bounce so you stay above this one bird. For some reason the bat comes out and lets you kill it anyway on level 19. On other levels this tactic is inadvisable because the bat won't come out until you get on the rope and you can easily lose all your lives as a result.